Cement kilns have been used to utilize waste materials to supply heat thereto and they function to destroy the liquified hazardous waste. Cement kilns function as excellent incinerators because they have operating temperatures which exceed 1800.degree. F. and the flame temperature of the primary burner exceeds 3000.degree. F. The residence time of combustion gases inside the kiln far exceeds the required two seconds specified by the EPA. Also, the large mass of reactive minerals travelling down the length of the kiln chemically binds with inorganics to provide a stabilizing effect and the turbulent flow of alkaline mineral dust within the combustion gases flowing down the kiln provides excellent scrubbing of the gases before they are discharged to the environment.
In my U.S. Pat. No. 5,257,586 issued Nov. 2, 1993, there is disclosed an improved method and apparatus for feeding solid waste materials to the interior of a cement kiln which has unique systems for the prevention of back-flashing of combustion in the feeding system and a system for delivering the solids to the interior of the rotating drum without interfering with the drum rotation.
Prior to the present invention, a mixture of liquid and semi-liquid (sludge) waste material has been delivered to the burner of a kiln as a means of destroying the hazardous waste and obtaining usable heat from such destructive burning. Other efforts have been made to supply such wastes pneumatically as dry and powdered solids into the primary burner of a kiln. These methods greatly limit the types and amounts of solid hazardous wastes which have been burned in kiln burners and industrial furnaces.